Decarbonylation process

ABSTRACT

A process is provided for the synthesis of furan and related compounds by liquid-phase decarbonylation of furfural and derivatives, using a palladium/metal aluminate catalyst. The compounds so produced can be used as starting materials for industrial chemicals for use as pharmaceuticals, herbicides, stabilizers, and polymers such as polyether ester elastomers and polyurethane elastomers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/238,270, filed Aug. 31, 2009, which is incorporated in its entiretyas a part hereof for all purposes.

FIELD OF DISCLOSURE

The disclosure relates to the manufacture of furan and relatedcompounds, and to the industrial use thereof for the synthesis of otheruseful materials.

BACKGROUND

Furan and related compounds are useful starting materials for industrialchemicals for use as pharmaceuticals, herbicides, stabilizers, andpolymers. For example, furan is used to make tetrahydrofuran,polytetramethylene glycol, polyether ester elastomers, and polyurethaneelastomers.

Known transition metal catalyzed, vapor-phase processes to produce furanby decarbonylation of furfural are limited by either the selectivity orlifetime of the supported catalyst. The conversion of furfural to furanis complicated by the tendency to form polymeric or carbonizingbyproducts which foul the catalyst surface and hinder the rate andlifetime of the catalyst. In the decarbonylation of furfural to furan,Pd has been shown to be an excellent catalyst for the reaction in boththe liquid and vapor phases. The challenge of this chemistry has beendeactivation of the catalyst from fouling reactions that are thought toproceed primarily through acid catalyzed oligomerization. Basic buffershave been added to the catalyst either as surface treatments (vaporphase) or as solid materials added to a liquid phase slurry reactor.Finding catalyst supports which enhance decarbonylation activity whileminimizing deactivation reactions such as carbon fouling is important tothe success of a Pd based process. Treating supports with basic buffersand base treatments has been shown to be effective in prior work, but asolid support that is active, stable and high temperature capable wouldhave high value in this technology.

Supported palladium catalysts are known to catalyze furfuraldecarbonylation reaction with high selectivity but are limited by shortlifetime. For example, U.S. Pat. No. 3,007,941 teaches a process for theproduction of furan from furfural comprising heating a liquid phaseconsisting essentially of furfural in the presence of palladium metaland a basic salt of an alkali metal; the basic salt is not part of thecatalyst per se but is continuously added to the liquid phase during thereaction. Also, U.S. Pat. No. 3,257,417 a process for production offuran comprising contacting liquid furfural with a palladium catalyst inthe presence of calcium acetate. Both these processes suffer from quickcatalyst deactivation and difficult catalyst regeneration processes.U.S. Pat. No. 3,223,714 teaches a continuous low pressure vapor phasedecarbonylation process for the production of furan comprisingcontacting furfural vapor with a supported palladium catalyst. Apreferred catalyst has about 0.3 wt % Pd supported on alumina. Thecatalyst can be regenerated in situ but the lifetime of a running cyclefor the catalyst is short and the production of furan per cycle is low.Catalysts which contain platinum and/or rhodium and to which cesium hasbeen added are preferably used.

Co-pending U. S. Provisional Patent Application 61/138,754 herebyincorporated by reference in its entirety, provides a process for thevapor-phase decarbonylation of furfural to furan using heating aPd/alumina catalyst that has been promoted with an alkali carbonate.

There remains a need for catalysts for the decarbonylation of furfuralto furan with improved lifetime and high productivity.

DESCRIPTION

The inventions disclosed herein include processes for the preparation offuran and related compounds and for the preparation of products intowhich those compounds can be converted.

Features of certain of the processes of this invention are describedherein in the context of one or more specific embodiments that combinevarious such features together. The scope of the invention is not,however, limited by the description of only certain features within anyspecific embodiment, and the invention also includes (1) asubcombination of fewer than all of the features of any describedembodiment, which subcombination may be characterized by the absence ofthe features omitted to form the subcombination; (2) each of thefeatures, individually, included within the combination of any describedembodiment; and (3) other combinations of features formed by groupingonly selected features taken from two or more described embodiments,optionally together with other features as disclosed elsewhere herein.Some of the specific embodiments of the processes hereof are as follows:

In one embodiment hereof, this invention provides a process for thesynthesis of a compound as represented by the following structure ofFormula (I)

by providing a compound as represented by the following structure ofFormula (II)

in the form of a gas, heating a Pd/metal aluminate catalyst, andcontacting the Formula (II) compound and the catalyst to produce aFormula (I) product; wherein R¹, R², and R³ are each independentlyselected from H and a C₁ to C₄ hydrocarbyl group.

In another embodiment hereof, a process is provided for preparing aFormula (I) product, as described above, that further includes promotingthe Pd/metal aluminate catalyst with an alkali carbonate.

In another embodiment hereof, a process is provided for preparing aFormula (I) product comprising providing a compound as represented byFormula (II) in the form of a liquid, and heating the Formula (II)compound in a reactor in contact with a Pd/metal aluminate catalyst. Inanother embodiment, this process further includes promoting the Pd/metalaluminate catalyst with an alkali carbonate.

In another embodiment hereof, a process is provided for preparing aFormula (I) product, as in any of the processes described above, thatfurther includes a step of subjecting the furan to a reaction (includinga multi-step reaction) to prepare therefrom a compound (such as thatuseful as a monomer), oligomer or polymer.

An advantageous feature of the processes hereof is the increasedlifetime and productivity of the Pd/metal aluminate catalyst and alkalicarbonate-promoted Pd/metal aluminate catalyst versus other catalystsused previously in the vapor phase.

In one embodiment of the processes described herein, R¹, R², and R³ allequal H; thus, the Formula (I) product is furan and the Formula (II)compound is furfural. The decarbonylation of furfural to produce furanmay then be represented by the following equation:

The Formula (II) compound used in the processes described herein ispreferably obtained from a biological material which is a good source ofhemicellulose. Examples include without limitation: straw, corn cobs,corn stalks (stover), sugar bagasse, hardwoods, cotton stalks, kenaf,oat hulls, and hemp. The Formula (II) compound, especially when it isfurfural, should be freshly distilled before use, since it can oxidizeand change color, producing undesirable high-boiling oxidation products.

In embodiments of the processes described herein, the decarbonylationreaction is catalyzed by a Pd/metal aluminate catalyst. As used herein,the term “metal aluminate” denotes a compound of alumina (Al₂O₃) with ametal oxide. This can be indicated explicitly by the chemical formula.For example, the formula for lithium aluminate, LiAlO₂ may be written asLi₂O.Al₂O₃ Such a catalyst support is intrinsically less acidic thanalumina. The use of such supports for the Pd which are intrinsicallyless acidic than Al₂O₃ can result in less carbonization of the catalystsurface, reducing the rate of catalyst deactivation and therebylengthening lifetime. Examples of suitable metal aluminates includewithout limitation aluminates of: alkali metals such as lithium, sodium,and potassium; alkaline earth metals such as calcium, barium, andstrontium; lanthanum; gallium; and yttrium. An alkali metal aluminatemay be prepared by reacting an alkali metal salt, such as an alkalimetal carbonate, with a reactive transition alumina such as .γ-alumina,at elevated temperatures, up to about 600° C.−700° C., for a period ofup to 24 hours, as described in U.S. Pat. No. 3,663,295. Other metalaluminates may be prepared analogously. In one embodiment, the catalystsupport is lithium aluminate, LiAlO₂ (CAS Registry No. 12003-67-7),which is available commercially (e.g., from Johnson Matthey, RoystonHerts, England).

In another embodiment of the processes described herein, thedecarbonylation reaction is catalyzed by a Pd/metal aluminate catalystthat has been promoted with an alkali carbonate, such as sodiumcarbonate (Na₂CO₃), potassium carbonate (K₂CO₃), or cesium carbonate(Cs₂CO₃). The alkali content of the catalyst is between about 1 andabout 100 mg per g catalyst. In some embodiments, the alkali content isbetween and optionally including any two of the following values: 1, 5,10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 mg per g catalyst. In oneembodiment, the alkali carbonate is cesium carbonate.

The catalyst is promoted by immersing a palladium/metal aluminatecatalyst in the form of powder, pellets, rods, spheres or any extrudedor pressed form in an aqueous solution of the alkali carbonate, withagitation. The concentration is the alkali carbonate solution notcritical and is generally in the range of about 0.1 to about 20 wt %.Optimal immersion time will depend on the surface area of thepalladium/metal aluminate catalyst, temperature, and alkali carbonateconcentration and is readily determined by one of ordinary skill in theart. In one embodiment, the palladium/metal aluminate catalyst isimmersed in a 5-10 wt % alkali carbonate solution at room temperaturefor about 4-6 hours. The wet catalyst is then removed from the solutionand dried, for example, for about 2-3 hours in an air oven at about110-130° C.; the catalyst may also be allowed to dry initially underambient conditions, before oven drying. The dried catalyst is calcinedat about 200 to 500° C. for about 2 to about 8 hours

The decarbonylation reaction may be conducted as a vapor (gas) phaseprocess or a liquid phase process. The terms “gas” and “vapor” are usedherein interchangeably. In a vapor phase process, the reaction isconducted by injecting the Formula (II) compound in gaseous form into areactor that is loaded with the desired catalyst. In one embodiment, theFormula (II) compound is provided in gaseous form by heating liquidFormula (II) compound to a temperature high enough to vaporize it; forfurfural, this is about 180° C. A non-reactive internal standard (e.g.,dodecane) may be present in the Formula (II) compound at about 0.5 wt %for analytical purposes, i.e., to confirm mass balance. Hydrogen may beco-fed to help volatilize the Formula (II) compound; hydrogen is alsoknown to extend catalyst life. Typical hydrogen feed rates are fromabout 0.25 to about 5.0 moles hydrogen per mole furfural. Water may alsobe added to the Formula (II) compound, either in the liquid compoundbefore it is volatilized or fed separately to either the liquid orgaseous Formula (II) compound, as described in co-pending U.S.Provisional Patent Application 61/138,754.

The reaction may occur in the gas phase at a temperature that cansuitably be in the range of from about 200° C. to about 400° C.,generally in the range of from about 270° C. to about 330° C. In someembodiments, the reaction temperature is between and optionallyincluding any two of the following values: 200° C., 220° C., 240° C.,260° C., 270° C., 280° C., 290° C., 300° C., 310° C., 320° C., 330° C.,340° C., 360° C., 380° C., and 400° C. The reaction temperature referredto here is the temperature that has been provided for the catalyst inthe catalyst zone of the reactor. A temperature in these ranges isprovided by heating the various portions of the reactor from a sourceexternal thereto, in particular a heating element designed to surroundand heat the catalyst zone of the reactor, and thus the catalyst itself.The selected temperature thus exists in the catalyst zone of the reactorupon the occasion when the furfural is contacted with the catalyst.

The vapor phase decarbonylation reaction is generally run at ambientpressure or slightly above. The pressure is not critical, as long as theFormula (I) and Formula (II) compounds remain in the gas phase in thereactor. The reaction residence time can be a minute or less; in someembodiments, the reaction time can be less than one second. In someembodiments, the reaction residence time is between and optionallyincluding any two of the following values (seconds): 0.5, 1, 2, 3, 4, 5,6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, and 60. The reactionis run with continuously fed Formula (I) compound and, preferably,hydrogen for a length of time suitable to determine the lifetime of thecatalyst. For example, a lifetime is calculated as the grams of furanproduced per gram of Pd in the reactor. A lifetime of greater than10,000 grams per gram Pd is desirable, greater than 100,000 grams per gPd more so. In all cases, however, the reaction is carried out at atemperature and pressure and for a time that is sufficient to obtaingas-phase production of the Formula (I) compound. The amount of Pd isnot critical; in one embodiment of the vapor phase process, it ispresent at 0.1 to 2.0 wt % (based on weight of total Pd+metalaluminate). In some embodiments, the amount of Pd is between andoptionally including any two of the following values (wt %): 0.1, 0.3,0.5, 0.7, 0.9, 1.1, 1.3, 1.5, 1.7, 1.9, and 2.0.

In a liquid phase embodiment of the decarbonylation process, thereaction is conducted by injecting a Formula (II) compound in liquidform into a reactor that is loaded with the desired catalyst. The powderform of the Pd/metal aluminate catalyst can be used in liquid phasedecarbonylation of Formula (II) compounds (e.g., furfural). In thiscase, higher Pd loadings are used. In some embodiments, the Pd loading(wt %) is between and optionally including any two of the followingvalues: 1, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9,9.5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20. Solids (catalyst)concentrations in the slurry reactor can be from 0.01 to 30 wt %; in oneembodiment, the concentration is between 0.5 and 5 wt % catalyst. Insome embodiments, the solids (catalyst) concentration (% by weight) isbetween and optionally including any two of the following values: 0.01,0.05, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9, 10, 12, 14,16, 18, 20, 22, 24, 26, 28, 29, and 30. The Pd/metal aluminate catalystpowder can also be used with a basic buffer powder in suspension, suchas sodium carbonate, potassium carbonate, or calcium acetate, asdescribed in U.S. Pat. No. 3,007,941 and U.S. Pat. No. 3,257,417.

When the Formula (II) compound is furfural, the reaction may occur inthe liquid phase at a temperature that is in the range of from about162° C. to about 230° C. In some embodiments, the temperature is betweenand optionally including any two of the following values: 162° C., 170°C., 175° C., 180° C., 185° C., 190° C., 195° C., 200° C., 205° C., 210°C., 215° C., 220° C., 225° C., and 230° C. The reaction temperaturereferred to here is the temperature that has been provided for thecatalyst in the catalyst zone of the reactor. A temperature in theseranges is provided by heating the various portions of the reactor from asource external thereto, in particular a heating element designed tosurround and heat the catalyst zone of the reactor, and thus thecatalyst itself. The selected temperature thus exists in the catalystzone of the reactor upon the occasion when the Formula (II) compound iscontacted with the catalyst. When the atmospheric boiling point of theFormula (II) compound is lower than the reaction temperature, as is thecase when the Formula (II) compound is furfural (boiling point about162° C.), the reaction is run at greater than atmospheric pressure, forexample, about 25 to 100 psi above atmospheric pressure. In addition toproviding reflux temperatures in the desired range, such pressuresfacilitate the condensation and separation of the Formula (I) compound(e.g., furan) from the carbon monoxide gas stream produced as reactionproceeds.

Reactors suitable for use in the processes hereof include fixed-bedreactors, and pipe, tubular or other plug-flow reactors and the like inwhich the catalyst particles are held in place and do not move withrespect to a fixed residence frame; or fluidized bed reactors. TheFormula (II) compound may be flowed into and through reactors such asthese on a continuous basis to give a corresponding continuous flow ofproduct at the downstream end of the reactor. These and other suitablereactors are more particularly described, for example, in Fogler,Elements of Chemical Reaction Engineering, 2nd Edition, Prentice-HallInc. (1992). In one embodiment, in-flow lines are heat traced to keepthe reactant at a suitable temperature, and the temperature of thecatalyst zone is controlled by a separate heating element at thatlocation. The Formula (I) product, as obtained from the reactor in theform of a gas, may be condensed by cooling to a liquid for ease offurther handling. Alternatively, the process may further comprisepurifying the Formula (I) product, such as by distillation. For example,the Formula (I) product may be fed directly into, e.g., a distillationcolumn to remove unreacted Formula (II) compound and other impuritiesthat may be present; the distilled product can then be isolated andrecovered.

The distilled product may also, however, be subjected with or withoutrecovery from the reaction mixture to further steps to convert it toanother product such as another compound (such as a type useful, forexample, as a monomer), or an oligomer or a polymer. Another embodimentof a process hereof thus provides a process for converting the Formula(I) product, through a reaction (including a multi-step reaction), intoanother compound, or into an oligomer or a polymer. For example, theFormula (I) product furan may be made from the Formula (II) compoundfurfural by a process such as described above, and then converted intotetrahydrofuran by hydrogenation. The tetrahydrofuran can in turn beused for preparation of polytetramethylene ether glycol, which in turncan be reacted with 1,4-butanediol and terephthalic acid to producepolyetherester elastomers, or with diisocyanates to producepolyurethanes.

All publications, patent applications, patents, and other referencesmentioned herein are incorporated by reference in their entirety. Unlessotherwise defined, all technical and scientific terms used herein havethe same meaning as commonly understood by one of ordinary skill in theart to which this invention belongs. In case of conflict, the presentspecification, including definitions, will control.

Although methods and materials similar or equivalent to those describedherein can be used in the practice or testing of the present invention,suitable methods and materials are described herein.

Unless stated otherwise, all percentages, parts, ratios, etc., are byweight.

When an amount, concentration, or other value or parameter is given aseither a range, preferred range or a list of upper preferable values andlower preferable values, this is to be understood as specificallydisclosing all ranges formed from any pair of any upper range limit orpreferred value and any lower range limit or preferred value, regardlessof whether ranges are separately disclosed. Where a range of numericalvalues is recited herein, unless otherwise stated, the range is intendedto include the endpoints thereof, and all integers and fractions withinthe range. It is not intended that the scope of the invention be limitedto the specific values recited when defining a range.

When the term “about” is used in describing a value or an end-point of arange, the disclosure should be understood to include the specific valueor end-point referred to.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “containing,” “characterized by,” “has,” “having” or anyother variation thereof, are intended to cover a non-exclusiveinclusion. For example, a process, method, article, or apparatus thatcomprises a list of elements is not necessarily limited to only thoseelements but may include other elements not expressly listed or inherentto such process, method, article, or apparatus. Further, unlessexpressly stated to the contrary, “or” refers to an inclusive or and notto an exclusive or. For example, a condition A or B is satisfied by anyone of the following: A is true (or present) and B is false (or notpresent), A is false (or not present) and B is true (or present), andboth A and B are true (or present).

Use of “a” or “an” are employed to describe elements and components ofthe invention. This is done merely for convenience and to give a generalsense of the invention. This description should be read to include oneor at least one and the singular also includes the plural unless it isobvious that it is meant otherwise.

The materials, methods, and examples herein are illustrative only and,except as specifically stated, are not intended to be limiting.

EXAMPLES

The advantageous attributes and effects of the processes hereof may beseen in a series of examples (Examples 1˜3), as described below. Theembodiments of these processes on which the examples are based arerepresentative only, and the selection of those embodiments toillustrate the invention does not indicate that conditions,arrangements, approaches, regimes, steps, techniques, configurations,protocols or reactants not described in these examples are not suitablefor practicing these processes, or that subject matter not described inthese examples is excluded from the scope of the appended claims andequivalents thereof.

Materials.

The following materials were used in the examples.

Pd/alumina catalyst (0.5% Pd, gamma alumina support, 3 mm pellets) wasobtained from the Engelhard Corporation, now BASF Catalysts LLC, adivision of BASF—The Chemical Company, Ludwigshafen, Germany. Pd/lithiumaluminate catalyst (0.5% Pd, lithium aluminate support, 3 mm pellets)was obtained from Johnson Matthey, Royston Herts, England.

Furfural was obtained from HHI, China, pre-distillation purity 98.5%. Itwas freshly distilled in a 20 plate 1 inch (2.54 cm) Oldershaw columnbatchwise prior to run with minimal air contact)

The meaning of abbreviations is as follows: “cm” means centimeter(s),“g” means gram(s), “GC” means gas chromatograph, “h” means hour(s), “kg”means kilogram(s), “mL” means milliliter(s), “min” means minutes, “mm”means millimeter(s), “psig” means pounds per square inch gauge, “THF”means tetrahydrofuran, and “vol” means volume.

Comparative Example A

This comparative example demonstrates the vapor-phase decarbonylation offurfural in the presence of an unpromoted Pd/alumina catalyst.

Approximately 2 grams of Pd/alumina catalyst (0.5% Pd on gamma aluminasupport, 3 mm pellets) was loaded onto a stainless steel mesh supportwithin a 18″×½″ (45.7 cm×1.3 cm) outside diameter (o.d.) type 316stainless steel tube reactor with inlets for gas and liquid feeds and aninternal thermocouple operating at atmospheric pressure. The catalystwas then pre-conditioned in situ in the reactor by flowing nitrogen gas,initially at room temperature, then raising the temperature to 270° C.over a period of 2 hours, while flowing hydrogen gas at 15 cm³/min, andintroducing the furfural feed (which included 0.5 wt % dodecane as aninternal standard) concurrently to generate reaction data. At reactiontemperature (270° C.), hydrogen flow was set at 17 mL/min and furfuralflow at 2.0 mL/h. The molar ratio of hydrogen to furfural was 2.0. Thegaseous product stream was kept at 180° C. and fed directly to anAgilent™ 6890 GC equipped with flame ionization and mass selectivedetectors. Furfural conversion (%) was calculated as follows: [(1−(area% furfural in product/area % dodecane in the product)/(area % furfuralin feed liquid/area % dodecane in feed liquid)] times 100. Furanselectivity (%) was calculated as follows: (moles of furan/moles offurfural reacted) times 100. THF, furfural alcohol and methyl-furanselectivity (%) were calculated analogously. Kilograms of furan producedper gram of Pd was calculated using the conversion, the furanselectivity and the amount of Pd in the reactor during the lifetimestudy. Initial furfural conversion was 99%, but it steadily droppedduring the run to 93% at 23 hours (3.06 kg furan per g Pd), and to 32%at 126 hours (7.87 kg furan per g Pd). Furan selectivity was 83%initially, with 12% selectivity to tetrahydrofuran (THF). At 23 hoursFuran selectivity was 92% with 3% selectivity to THF. At 126 hours, thefuran selectivity had dropped to 89% with 0.3% THF. Byproducts wereprimarily 2-methylfuran and furanmethanol, both from hydrogenation offurfural.

TABLE 1 Kg Furfural THF Furan Hours Furan per g Pd Conversion %Selectivity % Selectivity % 1 0.1 99 12 83 23 3.06 93 3 92 126 7.87 830.3 89

Comparative Example B

This example demonstrates preparation of a Cs₂CO₃-promoted Pd/aluminacatalyst.

The Pd/alumina catalyst described in Comparative Example A (0.5% Pd,20.3125 g) was immersed in 20 mL of a 7.5% aqueous solution of Cs₂CO₃(1.50 g Cs₂CO₃ in 20 mL deionized water) and gently agitated on anorbital shaker for 5 hours at room temperature. The mixture was filteredand the rods rinsed with deionized water (3×20 mL). The rods wereallowed to air dry. The catalyst was further dried in an oven at 120° C.in ambient air for 2 hours and cooled to room temperature for 1 hour andweighed. The rods were calcined at 300° C. for 4 hours and cooledovernight.

Comparative Example C

This example demonstrates the vapor-phase decarbonylation of furfural inthe presence of a Pd/alumina catalyst that was promoted with cesiumcarbonate.

The procedure similar to that described in Comparative Example A wascarried out using Pd/alumina catalyst that was treated with cesiumcarbonate using the procedure of Comparative Example B. Approximately 2grams of Pd/alumina catalyst (0.5% Pd on gamma alumina support, 3 mmpellets) was loaded onto a stainless steel mesh support within a 18″×½″(45.7 cm×1.3 cm) outside diameter (o.d.) type 316 stainless steel tubereactor with inlets for gas and liquid feeds and an internalthermocouple operating at atmospheric pressure. The catalyst was thenpre-conditioned in situ in the reactor by flowing nitrogen gas,initially at room temperature, then raising the temperature to 290° C.over a period of 2 hours, while flowing hydrogen gas at 15 cm³/min, andintroducing the furfural feed (which included 0.5 wt % dodecane as aninternal standard and 3% water by weight) concurrently to generatereaction data. At reaction temperature (290° C.), hydrogen flow was setat 17 mL/min and furfural flow at 2.0 mL/h. The molar ratio of hydrogento furfural was 2.0. The gaseous product stream was sampled bycondensing a 15 minute flow time in a chilled (−10 C) glass productbottle which contained 0.5 ml n-methyl pyrrolidone (NMP) for sampledilution. The sample was injected into an Agilent™ 6890 GC equipped withflame ionization and mass selective detectors. Furfural conversion (%)and product selectivity (%) were determined by GC analysis as describedin Comparative Example A. The initial furfural conversion was 99.2%. Thefurfural conversion was steady until approximately 139 hours (21.2 kgfuran per g Pd) when unconverted furfural began growing in the GCanalysis showing 87.1% conversion. The reactor temperature was thenraised to 310° C. to increase the furfural conversion. At 144.5 hoursthe furfural conversion was up to 94.6%. At 163.8 hours the conversionwas at 90.4% and the temperature was raised to 330 C for one more day ofoperation (25.8 kg furan per g Pd). The furfural feed was stopped at 171hours. Furan selectivity was 94.1% initially, with 4.8% selectivity totetrahydrofuran (THF). At 139 hours, furan selectivity was 97.8% with0.3% selectivity to THF. At 171 hours, the furan selectivity was 98.6%with minimal THF production. Less than 1% byproduct methylfuran andfuranmethanol was seen throughout the run.

TABLE 2 Furfural THF Furan Temperature, Kg Furan Conversion SelectivitySelectivity ° C. Hours per g Pd % % % 290 1 0.1 99.2 4.8 94.1 290 139.221.2 87.1 0.3 97.8 310 144.5 21.9 94.6 0.2 98.3 310 163.8 25.2 90.4 0.298.3 330 171 26.3 95.4 0.1 98.6

Example 1

This example demonstrates the vapor-phase decarbonylation of furfural inthe presence of unpromoted Pd/lithium aluminate catalyst.

The procedure described in Comparative Example C was carried out usingPd/lithium aluminate catalyst that was not pre-treated in any way.Furfural conversion and product selectivity (%) were determined by GCanalysis as described in Comparative Example A. The initial furfuralconversion was 100%. The furfural conversion was slowly decreasing untilapproximately 116 hours (17.5 kg furan per g Pd) when the conversion wasat 98.8% but selectivity to furfuryl alcohol (furanmethanol) had climbedto 2.5%. The reactor temperature was then raised to 310° C. to improvefurfural conversion and selectivity to furan. At 120 hours the furfuralconversion was up to 99.4% and furfuryl alcohol was down to 0.5%. At 169hours the conversion was at 88.5% and the temperature was raised to 330°C. for one more day of operation (27.1 kg furan per g Pd was reached).The furfural feed was stopped at 191 hours as conversion continued todrop. Furan selectivity was 70.4% initially, with 26% selectivity totetrahydrofuran (THF). At 120 hours, furan selectivity was 95.2% with2.5% selectivity to THF. At 169 hours, the furan selectivity was 93%with 1.3% THF production. Byproduct 2-methylfuran was initially at 1.7%,but dropped to below 0.5% after only 2 hours of operation and remainedlow throughout the run.

TABLE 3 Kg Furan Furfural THF Methyl Furan Furfuryl Alcohol FuranTemperature, per g Conversion Selectivity Selectivity SelectivitySelectivity ° C. Hours Pd % % % % % 290 1 0.1 100 26 1.7 0.0 70.4 290116 17.5 98.8 4.4 0.7 2.5 90.9 310 120 18.0 99.6 2.2 0.5 0.9 95.1 310169 24.9 88.5 1.3 0.5 3.5 93.0 330 191 27.1 67.5 0.6 0.4 2.3 95.6

Example 2

This example demonstrates the vapor-phase decarbonylation of furfural inthe presence of a Pd/Li-alumina catalyst that was promoted with cesiumcarbonate.

The procedure, similar to that described in Comparative Example A, wascarried out using Pd/Li-alumina catalyst that had been treated withcesium carbonate using the procedure of Comparative Example B.Approximately 2 grams of Pd/lithium aluminate catalyst (0.5% Pd onlithium aluminate support, 3 mm pellets) was loaded onto a stainlesssteel mesh support within a 18″×½″ (45.7 cm×1.3 cm) outside diameter(o.d.) type 316 stainless steel tube reactor with inlets for gas andliquid feeds and an internal thermocouple operating at atmosphericpressure. The catalyst was then pre-conditioned in situ in the reactorby flowing nitrogen gas, initially at room temperature, then raising thetemperature to 290° C. over a period of 2 hours while flowing hydrogengas at 15 cm³/min, and introducing the furfural feed (which included 0.5wt % dodecane as an internal standard and 3% water by weight)concurrently to generate reaction data. At reaction temperature (290°C.), hydrogen flow was set at 17 mL/min and furfural flow at 2.0 mL/h.The molar ratio of hydrogen to furfural was 2.0. The gaseous productstream was sampled by condensing a 15 minute flow time in a chilled(−10° C.) glass product bottle which contained 0.5 mL n-methylpyrrolidone (NMP) for sample dilution. Furfural conversion and productselectivity (%) were determined by GC analysis as described inComparative Example A. The results, shown in Table 4, demonstrate alonger lifetime with alkali-promoted Pd on lithium aluminate than seenon alkali-promoted alumina as well as non promoted Li-aluminate. Thealkali carbonate treatment significantly reduced hydrogenation activityin the decarbonylation process.

TABLE 4 Kg Furfural Furfuryl Furan Conver- THF Alcohol Furan Temp per gsion Selectivity Selectivity Selectivity ° C. Hours Pd % % % % 290 10.16 100 1.0 0.0 97.6 290 120 18.3 95.0 0.1 4.2 95.0 310 149 22.4 95.00.0 2.6 96.3 310 196.8 29.5 95.6 0.1 3.4 95.5 310 287 42.7 92.0 0.1 2.896.1

Example 3

This example demonstrates the liquid-phase decarbonylation of furfuralto furan using a Pd/metal aluminate catalyst.

Dry furfural (60.07 g) and catalyst (0.3 g, 5% Pd on alumina/lithiumaluminate) were charged to a 100-mL stainless steel Parr reactorequipped with a mechanical agitator, furfural feed line and verticalstainless steel condenser, contained by a pressure-regulated vent valve.The vertical condenser was maintained at a temperature to returnunreacted furfural to the reactor while allowing furan and carbonmonoxide vapor to pass through the pressure-regulated vent valve, afterwhich the furan product was condensed, and the carbon monoxideproduction rate was measured using a mass flow meter.

The reaction charge was heated, and the temperature was automaticallycontrolled at about 190° C. The pressure-regulated vent valve wasadjusted to maintain about 21 psig pressure on the reactor contents. Thereaction was run substantially according to the procedure described inExample 1 of U.S. Pat. No. 3,257,417, except that the temperature wasabout 190° C. instead of about 215° C. and the pressure was about 21psig instead of about 67 psig. Furfural was initially fed to the reactorat a rate of about 7.5 mL/h. The measured carbon monoxide productionrate with time showed about a 75% decrease in catalyst activity overabout 20 h of reaction time. The initial rate of 231 g furan per g Pdper hour dropped to about 49 after 20 h.

It is to be appreciated that certain features of the invention whichare, for clarity, described above and below in the context of separateembodiments, may also be provided in combination in a single embodiment.Conversely, various features of the invention that are, for brevity,described in the context of a single embodiment, may also be providedseparately or in any subcombination. Further, reference to values statedin ranges includes each and every value within that range.

What is claimed is:
 1. A process for the synthesis of a compound as represented by the following structure of Formula (I)

by providing a compound as represented by the following structure of Formula (II)

in the form of a liquid and heating the Formula (II) compound in contact with a Pd/metal aluminate catalyst in a reactor to produce a Formula (I) product; wherein R¹, R², and R³ are each independently selected from H and a C₁ to C₄ hydrocarbyl group.
 2. The process according to claim 1 wherein R¹, R², and R³ are each H.
 3. The process according to claim 1 wherein the substituted alumina is an alkali metal aluminate, an alkaline earth metal aluminate, gallium aluminate, lanthanum aluminate, or yttrium aluminate.
 4. The process according to claim 3 wherein the alkali metal aluminate is LiAlO₂.
 5. The process according to claim 1 wherein contacting the Formula (II) compound and the catalyst to produce a Formula (I) product occurs in the liquid phase at a temperature that is in the range of from about 162° C. to about 230° C., and at a pressure that is about 25 to 100 psi above atmospheric pressure.
 6. The process according to claim 1 wherein the Pd loading of the Pd/substituted alumina catalyst is about 1 to about 20% by weight.
 7. The process according to claim 1 wherein the catalyst concentration in the reactor is from about 0.01 to about 30 wt %.
 8. The process according to claim 1 wherein the reaction is carrier out in the presence of a basic buffer powder in suspension.
 9. The process according to claim 1, further comprising purifying the Formula (I) product.
 10. The process according to claim 9, wherein the Formula (I) product is purified by distillation.
 11. The process according to claim 1 further comprising a step of subjecting the Formula (I) compound to a reaction to prepare therefrom a compound, oligomer or polymer. 